Top Democrats pressed for Attorney General Jeff Sessions to resign on Thursday after a newspaper reported he had not disclosed two meetings with the Russian ambassador before President Donald Trump took office. Sessions, a top adviser to Trump during the presidential campaign, received Russian Ambassador Sergei Kislyak in his office in September, the Washington Post reported. That was at the height of what U.S. intelligence officials say was a Russian hacking campaign to influence the November election in the Republican candidate's favor.The other encounter was in July at a Heritage Foundation event that was attended by about 50 ambassadors, during the Republican National Convention, the Post said. A Justice Department official confirmed Sessions' contacts in July and September.Allegations over contacts between Trump aides and Russia before his inauguration, and the charge of Russian meddling, have swirled around the early days of Trump's presidency. Trump has accused former officials in the administration of former President Barack Obama of trying to discredit him.Nancy Pelosi, the top Democrat in the House of Representatives, called for Sessions to resign and for an independent, bipartisan investigation into Trump's possible ties to Russians."Sessions is not fit to serve as the top law enforcement officer of our country and must resign," she said in a statement late on Wednesday.U.S. Representative Elijah Cummings criticized Sessions for keeping his contact with the ambassador secret even after Trump fired his first national security adviser, Michael Flynn. Sessions "should resign immediately," he said.Flynn was dismissed last month after it emerged that he had discussed U.S. sanctions on Russia with Kislyak before Trump's swearing-in on Jan. 20, and then misled Vice President Mike Pence about the conversations.At his Jan. 10 confirmation hearing in the U.S. Senate, Sessions said he had no contact with Russian officials about the 2016 election. In a statement late on Wednesday, Sessions said he had never discussed campaign details with any Russian officials."I have no idea what this allegation is about. It is false," Sessions saidThe White House dismissed the revelation as a partisan attack. "Attorney General Sessions met with the ambassador in an official capacity as a member of the Senate Armed Services Committee, which is entirely consistent with his testimony. "The Russian Embassy to the United States, shrugging off the uproar, said on Thursday it was in regular contact with "U.S. partners."The revelation of Sessions' contacts fueled new congressional calls for the appointment of a special counsel to investigate Russia's role in the 2016 presidential election.Before Trump took office, U.S. intelligence agencies concluded that Russia had sought to influence the campaign, including by hacking into and leaking Democratic emails. The Kremlin has denied the allegations.As attorney general, Sessions oversees the Justice Department, including the FBI, which has been leading investigations into the allegations of the Russian meddling and any links to Trump's associates.Sessions, a former senator, has so far resisted calls to recuse himself from those investigations. On Thursday morning, he told NBC News, "Whenever it's appropriate I will recuse myself, there's no doubt about that."REPUBLICAN CONCERNSessions' failure to disclose the contacts worried even some of his fellow Republicans.Republican, Representative Jason Chaffetz, chairman of the House Oversight Committee, said on Twitter "AG Sessions should clarify his testimony and recuse himself."During Sessions' confirmation hearing, Democratic Senator Al Franken asked him what he would do if he learned of any evidence that anyone affiliated with the Trump campaign communicated with the Russian government in the course of the 2016 campaign.Sessions said he was not aware of any such activities, adding, "I have been called a surrogate at a time or two in that campaign and I did not have communications with the Russians."Asked by Democrat Patrick Leahy in a questionnaire whether he had been in contact with "anyone connected to any part of the Russian government about the 2016 election, either before or after Election Day," Sessions responded, "No."Republican Lindsey Graham, a leading foreign policy voice in the Senate, said on CNN on Wednesday night if the FBI finds anything criminal in nature in its Russia-related investigations, a special prosecutor would be required."If that day ever comes, I'll be the first one to say it needs to be somebody other than Jeff," Graham said.Sessions' colleague on the Armed Services Committee, Democratic Senator Claire McCaskill, questioned why Sessions would meet with Kislyak."I've been on the Armed Services Com for 10 years. No call or meeting w/Russian ambassador. Ever. Ambassadors call members of Foreign Rel Com," she said in a Twitter post on Thursday.